The present invention relates generally to an EMC sealing system and method for an electrical enclosure. More particularly, the present invention is directed to a dynamic EMC sealing system incorporated with a docking cassette for printed circuit boards that provides a level of EMC shielding.
The past twenty-five or so years have seen the development of ever smaller electrical circuit components at the chip level. However, to take fullest advantage of achievements in electrical circuit miniaturization, one must package the resultant printed circuit cards containing these chips in an efficient manner. Clearly, the packaging of printed circuit cards in tight spaces is a direct logical extension of increasing chip level circuit densities. It should also be noted that the tight packaging of integrated circuit chips on printed circuit cards and the correspondingly dense packaging of the printed circuit cards is a design goal that is carried out for more than just the convenience of compactness. Compactness provides shorter distances between circuit components which, in turn, serves the very desirable goal of being able to operate the circuits effectively at higher frequencies, thus increasing the speed of numerous different forms of electrical systems, including but not limited to data processing systems.
Moreover, mainly for reasons associated with long-term system operation and reliability, it is likewise very desirable to be able to easily insert and remove these printed circuit cards even when they are disposed in very tight spaces. The insertion and removal operations are also provided as an important part of a xe2x80x9chot-pluggabilityxe2x80x9d function which is very desirable for xe2x80x9con the flyxe2x80x9d repairs, replacements, maintenance and upgrades. Accordingly, to whatever extent possible, packaging designs should be: economical to produce; function smoothly, require little or no maintenance; be producible from inexpensive, readily available materials; and be reliably operable over a large number of insertion and removal operation cycles.
Yet one other concern arises in electrical systems as circuit feature size shrinks, operating frequencies increase and packaging densities grow larger, namely, the generation of electromagnetic interference (EMI). Electronic circuit packaging designs should thus also be compatible with structures and configurations that are employed to prevent the leakage of electromagnetic interference. To whatever extent possible, packaging designs should also include structures which actually contribute positively to the containment of electromagnetic interference. There is an ever increasing problem of electromagnetic interference caused by such devices. Virtually every electronic device, intentionally or not, emits some form of electromagnetic radiation. While this condition could be tolerated when few devices existed, the increasing number of electronic devices has made the problem more acute. The problem has been exacerbated by the xe2x80x9cimprovementxe2x80x9d in semiconductor devices which allows them to operate at higher speeds, generally causing emission in the higher frequency bands where interference is more likely to occur. Successful minimization of the interference problem, sometimes referred to as xe2x80x9celectromagnetic compatibilityxe2x80x9d or xe2x80x9cEMCxe2x80x9d, generally requires that emissions from a given device be reduced by shielding and other means, and shielding be employed to reduce the sensitivity of a device to fields from other devices. Since shielding helps to reduce sensitivity to external fields as well as reduce emissions from the device, it is a common approach to a solution of the problem.
In newer high speed packages it is necessary to use a metallic type of gasket to provide better conduction with an electrical enclosure in which the printed circuit cards are engaged. However, use of known metallic gaskets are susceptible to damage such as bending or breaking. The gasket is commonly xe2x80x9cdamagedxe2x80x9d as a result of over deflection of the gasket. Once the metallic gasket is damaged, the gasket does not provide the intended function. Moreover, if the gasket actually breaks, the gasket poses a threat for a potential short.
It is also noted that the present discussion refers to printed circuit boards and printed circuit cards. As contemplated herein, the printed circuit board is the larger component into which at least one printed circuit card is inserted for purposes of electrical connection. The present disclosure places no specific limits on either the size of a printed circuit board or the size of a printed circuit card. In the most general situation, a circuit board will be populated with a plurality of printed circuit cards. That is, the printed board will have a number of printed circuit cards inserted therein.
Accordingly, as used herein, the terms xe2x80x9cprinted circuit boardxe2x80x9d and xe2x80x9cprinted circuit cardxe2x80x9d are considered to be relative terms.
Accordingly, the present inventors are presented with the following sometimes competing packaging problems: dense and close packaging, electromagnetic interference shielding, hot pluggability, the desire to provide an easy-to-load cartridge for carrying printed circuit cards, the removal of fully populated printed circuit boards and the insertion thereof, and means to provide a dynamic cooperative EMI shielding arrangement in a system which also provides repeated circuit board insertion and removal of these printed circuit cards therefrom without damage to the arrangement.
An apparatus for providing an electromagnetic conduction seal in a device disposed within an electrical enclosure is disclosed. The apparatus includes a metal EMC gasket defined by a first end and an opposite second end. The first end is operably secured to the device and at least the second end is allowed to float while remaining in electrical contact with the device. A lock strip is fixed to the device and is configured to provide limits of deflection of an intermediate portion of the gasket intermediate the first and second ends and captivate at least one floating end of the gasket. The intermediate portion provides an electromagnetic conduction seal between the device and with at least one of another device and/or the electrical enclosure.
In another embodiment, a method for providing an electromagnetic conduction seal in a device disposed within an electrical enclosure is disclosed. The method includes configuring a metal EMC gasket defined by a first end and an opposite second end, the first end is operably secured to the device, at least the second end is allowed to float while remaining in electrical contact with the device; fixing a lock strip to the device; configuring the lock strip to provide limits of deflection of an intermediate portion of the gasket intermediate the first and second ends; and captivating at least one floating end of the gasket, wherein the intermediate portion provides an electromagnetic conduction seal between the device and with at least one of another device and/or the electrical enclosure.